Stock-Based Compensation - Restricted Stock Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares (in 000’s)
Non-vested at beginning of period (in shares)	225	266	285
Granted (in shares)	77	138	155
Vested (in shares)	(146)	(178)	(171)
Forfeited (in shares)	(3)	(1)	(3)
Non-vested at end of period (in shares)	153	225	266
Weighted-Average Grant Date Fair Value
Non-vested at beginning of the year (in dollars per share)	$ 51.31	$ 39.28	$ 24.64
Granted (in dollars per share)	63.30	53.64	51.29
Vested (in dollars per share)	51.10	35.09	25.78
Forfeited (in dollars per share)	60.17	63.19	37.78
Non-vested at end of the year (in dollars per share)	$ 57.43	$ 51.31	$ 39.28